In many online systems, individuals provide services for each other; the recipient of the service obtains a benefit but the provider of the service incurs a cost. If benefit exceeds cost, provision of the service increases social welfare and should therefore be encouraged but the individuals...

<Para ID="Par1">Markets typically have many ways of learning about quality, with two of the most important being reputational forces and certification, and these types of learning often interact with and influence each other. This paper is the first to consider markets where learning occurs through these...</para>